Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
  • F01L1/00—Valve-gear or valve arrangements, e.g. lift-valve gear
  • F01L1/02—Valve drive
  • F01L1/04—Valve drive by means of cams, camshafts, cam discs, eccentrics or the like
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
  • F01L1/00—Valve-gear or valve arrangements, e.g. lift-valve gear
  • F01L1/02—Valve drive
  • F01L1/04—Valve drive by means of cams, camshafts, cam discs, eccentrics or the like
  • F01L1/047—Camshafts
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21D53/00—Making other particular articles
  • B21D53/84—Making other particular articles other parts for engines, e.g. connecting-rods
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21D53/00—Making other particular articles
  • B21D53/84—Making other particular articles other parts for engines, e.g. connecting-rods
  • B21D53/845—Making camshafts

Definitions

• This invention relates to a tubular fabricated camshaft for a reciprocating piston machine, such as an internal combustion engine or a compressor, wherein a plurality of camshaft elements are secured to a central tubular member passing through such elements.
• the elements comprise cams and may also comprise bearings, gears etc. all of which are secured to and axially spaced along the central tubular member.
• Camshafts have conventionally been produced as either castings or forgings, usually of steel, and have .' comprised a solid central member having a plurality of axially spaced integral cams and bearings thereon.
• advantages are to be gained in manufacturing camshafts as fabrications of separate elements wherein the cams and bearings are initially pre-formed to shape and then assembled on and secured at predetermined positions along the length of a central tubular shaft.
• Such fabricated tubular camshafts offer the advantages, when compared with solid cast or forged camshafts, of weight reduction; facilitation of lubricant supply to the cam and bearing surfaces from the hollow interior of the shaft and the possibility of selecting different materials for the cam, bearing and shaft.
• GB-A-275842 (Yassenoff) teaches the welding of preformed cam rings and bearing rings to a central tubular shaft wherein the cams, apart from a central aperture, may be solid or may be formed from drawn tubing or from strips of metal bent to a required cam profile.
• GB-A-1115093 (GKN Screws & Fasteners Limited) teaches the mechanical locking of preformed cam rings to a central tubular shaft, the cam rings being of substantially constant wall thickness and formed by drawing a tube to the desired cam profile and then cutting portions off the drawn tube to provide the individual cam rings.
• each cam ring is mechanically locked to the shaft at a desired axial position and angular orientation by a key engaged within the hollow cam ring nose and within an aperture in the shaft wall; each cam ring optionally being further secured to the shaft by an adhesive, or by soldering, brazing or welding.
• GB-A-1117816 (GKN Screws & Fasteners Limited) teaches the securing of centrally apertured preformed solid cam and bearing elements to a central tubular shaft by radially outwardly deforming the shaft into gripping engagement within the cam and bearing apertures.
• Such radially outward deformation of the shaft is taught as being accomplished by drawing an oversize mandrel through the shaft or by expanding the shaft by fluid pressure or explosive forming techniques.
• the central aperture of each solid cam or bearing is recessed radially outwardly, effectively to provide a spline arrangement, to enhance a secure gripping engagement between the radially outwardly expanded part of the shaft and the cams and bearings.
• JP-A-7644/1971 (Nakamura et al) teaches the securing of preformed cam rings to a central tubular shaft by fluid pressure radially outward expansion of the shaft into the hollow interior of each cam ring.
• the fluid pressure is applied to one end of the tubular shaft (the other end being sealed) whilst the preformed cam rings are held in predetermined axial spacing and angular orientation relative to the shaft in a closed die having cam recesses corresponding to and accommodating the cam rings in their desired positions.
• JP-A-7644/1971 A similar teaching to that of JP-A-7644/1971 is contained in GB-A-1530519 (Klockner Humboldt Deutz AG) wherein a central tubular shaft is radially outwardly expanded either by hydraulic, electro-hydraulic or mechanical means into the hollow interiors of preformed cam rings of substantially constant wall thickness.
• a method of producing a camshaft having a central tubular shaft and a plurality of cam rings spaced axially therealong characterised in that the cam rings are of initially circular cross sectional form and are assembled in axially spaced relation around the tubular shaft in a forming tool and that the forming tool is closed to press each of the initially circular cross section cam rings to a desired cam profile whilst deforming the tubular shaft relative to the cam rings whereby the cam rings are retained on the shaft against axial and angular displacement relative thereto.
• a fabricated camshaft comprising a plurality of cam rings axially spaced along a central tubular shaft wherein each cam ring is retained on the shaft against axial and angular displacement relative to an associated portion of the shaft which is deformed relative to the cam ring, said portion of the shaft having been mechanically deformed relative to the cam ring during pressing of the cam ring to its desired cam profile from an initially circular cross section cam ring located about the initially undeformed shaft.
• the fabricated camshaft, and method for its production differs from all of the prior art teachings referred to above in that the cam rings are formed from an initially circular cross section to a desired cam profile solely by being pressed within the forming tool in a predetermined axially spaced relationship about the central tubular shaft whilst, during the same pressing operation, the shaft is deformed relative to the "cam rings whereby the cam rings are retained on the shaft against axial and angular displacement relative thereto.
• the circular cam rings are provided initially as portions of predetermined axial dimension cut from a relatively inexpensive circular cross section tube;
• the circular cam rings can be assembled on the central tubular shaft and easily axially located in cam forming dies of the forming tool whereas, when the cam rings were preformed to a desired cam profile as taught by the prior art before being assembled on the central tubular shaft, it was then comparatively difficult to locate the cam rings accurately within cam profile cavities of a jig or the like prior to the securing of the rings to the shaft whether by welding, mechanical radially outward deformation of the shaft or fluid pressure deformation of the shaft.
• the pressing of the cam rings and deformation of the shaft may be carried out with the cam rings and the shaft at ambient temperature.
• the initially circular cam rings may be heated prior to their assembly around the shaft and then cooled to achieve an interference fit relative to the shaft either before, during or after the pressing of the cam rings and deformation of the shaft in the forming tool.
• the method according to the invention may include the additional step of further deforming the tubular shaft relative to the cam rings by fluid pressure applied internally of the shaft.
• further deformation of the shaft is carried out in a further forming tool having an axially extending central cavity and a plurality of cam shaped cavities into which fit the shaft and the cam rings respectively; the interior dimensions of the cam shaped cavities being in excess of the exterior dimensions of the cam rings whereby, upon the application of fluid pressure internally of the shaft, the cam rings are elastically deformed and the shaft is plastically deformed.
• the method of the invention conveniently also includes the additional step of subjecting the camshaft to a heat treatment process to harden the cam rings.
• the method may also include the additional step of further attaching the cam rings to the tubular shaft by a method employing brazing, soldering, hot welding (gas, electric arc, laser or electron beam) , cold welding, dipping, gluing, pinning, mechanical interlocking or any other suitable attachment method.
• a further attachment method may conveniently be carried out during the said heat treatment process, such method comprising the melting of a braze or solder metal prepositioned between the shaft and the cam ring.
• FIG. 1 is a somewhat diagrammatic isometric view of a camshaft constructed in accordance with the invention
• Figure 2 is an isometric view of one end of the camshaft shown in Figure 1 showing in more detail the deformation of the central tubular shaft relative to the cam rings;
• Figure 3 is a longitudinal cross sectional view through that part of the camshaft shown in Figure 2;
• Figure 4 is a diagrammatic transverse cross sectional view of a circular cam ring assembled around a central tubular shaft at a cam forming die position of a forming tool before the tool is closed;
• Figure 5 is a cross sectional view similar to that of Figure 4 but showing the tool in its closed position whereby the initially circular cam ring has been pressed to a desired cam profile and the shaft has been deformed relative to the cam ring;
• Figure 6 is a similar transverse cross sectional view of the formed cam ring on the deformed shaft (as shown in Figure 5) but located within a cooperating die cavity in a further forming tool for the application of fluid pressure to the interior of the shaft;
• Figures 7 and 8 are diagrammatic cross sectional views of a formed cam ring on a deformed shaft located within a further forming tool similar to that shown in Figure 6 but wherein the cooperating die cavity is modified thereby to modify the effect of the fluid pressure applied internally of the shaft.
• a camshaft produced in accordance with the invention and comprising, in this example, a central tubular shaft 10 upon which are mounted eight cam rings 12 of predetermined cam profile and five bearing journals 14 of circular profile; the tubular shaft being radially deformed relative to the cam rings whereby the rings are retained on the shaft against axial and angular displacement relative thereto.
• each of the cam rings 12 is retained on the shaft 10 is illustrated diagrammatically in Figure 4.
• a central tubular shaft 10 of uniform circular cross sectional form which is conveniently formed of a low carbon steel although it could be formed of aluminium or any other suitable plastically deformable material.
• a cam ring 12 of circular cross sectional form and constant wall thickness which is of a slightly greater internal diameter than the external diameter of the tubular shaft; the cam ring being provided as a "slice" cut from a length of tubing of uniform circular cross sectional form.
• the material of the tube from which the cam ring s cut is conveniently a high strength hardenable ductile steel or other steel suited to cam performance.
• FIG 4 Also shown in Figure 4 are two opposed parts 16 and 18 of a forming tool including respective opposed cam forming die cavities 20 and 22 in the two parts of the tool; the cavity 20 being to the desired cam profile and the cavity 22 being semi-circular.
• the necessary number of circular cam rings 12 and circular bearing journals 14 are assembled on the central tubular shaft 10 with each cam ring and bearing journal located respectively in a corresponding die cavity 22.
• the tool is then closed to the position shown in Figure 5 whereby the initially circular cam rings 12 are each pressed to the cam profile defined by the shape of the cam forming die cavity 22-22.
• the central tubular shaft 10 is deformed radially within each hollow cam ring essentially to the shape shown in Figure 5 whereby the cam rings are retained on the shaft against axial and angular displacement relative thereto.
• each of the radially deformed portions 24 of the tubular shaft 10 may not be deformed precisely to the shape shown in Figure 6; for example, each deformed portion may not entirely fill the hollow interior of its associated cam ring.
• the parts 26 of the shaft located axially between adjacent cam rings, or between a cam ring and a bearing journal, are retained in the forming tool in a cooperating generally cylindrical cavity against deformation during closure of the forming tool although, as may be best seen in Figure 3, the tubular shaft may become deformed radially outwardly around at least part of its periphery to provide radially outwardly extending bulges 28 on each axially outer side of a cam ring or bearing journal to provide an additional retention of the respective cam ring or journal against axial movement relative to the shaft.
• the mechanical pressing operation described above may be carried out with all of the elements of the camshaft maintained at ambient temperature i.e. the production of the camshaft is carried out by a cold pressing operation.
• each of the initially circular cam rings, and the bearing journals may be heated prior to their assembly on the central tubular shaft and then cooled either before, during or after the mechanical pressing operation to achieve an interference fit of the cam rings and bearing journals relative to the shaft.
• the internal diameters of the initially circular cam rings and of the bearing journals are slightly less than the external diameter of the central tubular shaft.
• the cam rings and bearing journals may be further secured to the central shaft by brazing, soldering, hot welding (e.g. gas, electric arc, laser or electron beam), cold welding, dipping, gluing, pinning. mechanical interlocking or by any other suitable securing method.
• the retention of the cam rings in particular may be enhanced by the application of fluid pressure applied internally to the central tubular shaft 10 in a further forming tool.
• fluid pressure applied internally of the central tubular shaft 10, after the die parts 30 and 32 have been closed and locked together, whereby the shaft -is radially outwardly expanded by the application of the fluid pressure.
• the tubular shaft 10 is plastically deformed whereas the cam rings 12 are elastically deformed due to the fact that the die cavities 34-36 have interior dimensions in excess of the exterior dimensions of the cam rings thereby permitting limited radially outward elastic expansion of the cam rings.
• the elastically deformed cam rings will then contract back onto the plastically deformed central tubular shaft.
• each of the die cavities 34-36 of the further forming tool is modified as shown in Figures 7 or 8 wherein, in Figure 7, diametrically opposed shims 38 have been located across the cam width in each of the upper and lower die parts 30 and 32 whereas, in Figure 8, the shims have been located across the parting line of the die parts.
• each of the cam rings 12 is pressed from its initially circular cross section form substantially to its final desired cam profile in the mechanical forming tool diagrammatically illustrated in Figure 4. No further substantial machining of the cam rings is required although a light finish machining may be applied. It will generally be desirable to .apply some form of heat treatment either locally to the whole, or to selected portions, of each cam ring or as a bulk heat treatment to the complete camshaft.
• Such a bulk heat treatment can harden the cam rings but not the central tubular shaft as their chemical compositions, and thus their reaction to hardening and tempering, will differ although it will be appreciated that a bulk heat treatment must be carried out before any radial expansion step (such as that described with reference to Figures 6 to 8) otherwise such a heat treatment may relax the assembled components to such an extent that the cam rings 12 become loosened from the central tubular shaft 10.
• the cam rings and central tubular shaft may be heated to a temperature within the range 850 degrees C to 900 degrees C and it is thus convenient, whilst the components are at this elevated temperature, to carry out the optional additional securing step referred to above by brazing or soldering.
• a brazing process could be carried out by pre-positioning a foil or strip of braze metal between the cam rings and the central tubular shaft before the initial mechanical pressing operation; said braze metal then melting during the bulk heat treatment step to braze the cam rings (and the bearing journals if desired) onto the central tubular shaft.
• any subsequent fluid pressure expansion step need not further deform those portions of the central tubular shaft fully into the hollow, interior of each cam ring.
• a piece of filler material such as a steel bar may be initially located within each cam ring below the cam nose position so as to provide extra rigidity to the cam nose when formed.
• a plurality of axially spaced apart cam rings of initially circular cross sectional form will be assembled onto a central tubular shaft within the forming tool with a said cam ring located at each of a plurality of corrresponding cam forming die cavities within the forming tool. Assembly of the initially circular cam rings (and the circular bearing journals) on the central tubular shaft within the forming tool is thus greatly facilitated in that it is only necessary to locate the cam rings and bearing journals at the respective die cavities; there being no necessity accurately to locate any of the components angularly relative to the central shaft before the forming tool is closed.
• the cam rings themselves are susceptible of low production cost in that they are produced simply as cut sections or "slices" of predetermined axial dimension from a relatively inexpensive circular cross section tube stock.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Valve-Gear Or Valve Arrangements (AREA)
• Gears, Cams (AREA)

Priority Applications (4)

Applications Claiming Priority (4)

Publications (1)

Family

ID=26291027

Family Applications (1)

Country Status (9)

Cited By (10)

Families Citing this family (8)

Citations (3)

• 1987
  • 1987-07-03 CA CA000541263A patent/CA1289776C/en not_active Expired - Lifetime
  • 1987-07-09 BR BR8707744A patent/BR8707744A/pt unknown
  • 1987-07-09 WO PCT/GB1987/000484 patent/WO1988000643A1/en active IP Right Grant
  • 1987-07-09 JP JP62504048A patent/JPH02501323A/ja active Granted
  • 1987-07-09 EP EP87904397A patent/EP0313565B1/en not_active Expired - Lifetime
  • 1987-07-10 ES ES8702045A patent/ES2007075A6/es not_active Expired
  • 1987-07-11 CN CN87104854A patent/CN1009570B/zh not_active Expired
• 1988
  • 1988-03-11 KR KR1019880700269A patent/KR880701813A/ko not_active Application Discontinuation
  • 1988-07-09 GB GB8828529A patent/GB2211127B/en not_active Expired - Lifetime

Patent Citations (3)

Also Published As

Similar Documents

Legal Events